Claude Opus 5.5 shipped on 22 September and Sonnet 5.5 on 28 September, and both carry the same note: on the Claude API and Google Cloud, the earlier computer_20251124 computer use tool is not accepted. It returns a 400.
When Claude Computer Use left beta in August, Anthropic said earlier versions remained available, and that was true. What has changed is that staying on the old tool now means staying on older models. The deprecation was never announced as one; it arrived as a property of each new release.
If you pinned computer_20251124 to avoid the migration — the request shape and tool handling both changed — that decision now has a cost it did not have six weeks ago. Worth checking before someone upgrades a model string and discovers it at runtime.